1. Field of the Invention
The present invention relates to a color picture tube, for example used as a television receiver or a computer monitor.
2. Related Background Art
FIG. 2 is a schematic sectional view of a color picture tube in common use.
In FIG. 2, a color picture tube 1 has an envelope composed of a face panel 3 having an inner face on which a phosphor screen 2 is formed and a funnel 4 bonded to the rear part of the face panel 3, which includes a color selecting electrode 5 opposed to the phosphor screen 2, a frame 6 supporting the color selecting electrode 5, and an electron gun 8 provided in a neck portion 7 of the funnel 4. Three electron beams 9 (the electron beams overlap one another so as to be seen as one electron beam in the figure) are emitted from the electron gun 8. The electron beams 9 pass through a plurality of apertures provided on the color selecting electrode 5 while being deflected by a deflection yoke 10 provided at an outer portion of the funnel 4 to land on the phosphor screen 2.
FIG. 8 schematically shows a state of a color selecting electrode and a phosphor screen of a conventional color picture tube. On a color selecting electrode 5, a plurality of apertures 11 of substantially slot shape are formed. On a phosphor screen 2, blue-, green-, and red-emitting phosphor lines 12b, 12g, and 12r of substantially a given width are arranged in the form of stripes. When the color picture tube is in operation, three electron beams pass through the apertures 11 to land at the phosphor screen, so that the phosphor lines 12b, 12g, and 12r are irradiated with beams 13b, 13g, and 13r that have passed through the apertures 11. Then, irradiated portions 14 of the phosphor lines 12b, 12g, and 12r emit light, and thus an image is formed.
However, the conventional color picture tube with the phosphor screen described above has presented a problem of a limit to improvements in luminance.
When electron beams pass through the apertures of the color selecting electrode to be irradiated onto the phosphor lines, bridges 15, each provided between the adjacent apertures 11 in a vertical direction (a direction along the phosphor lines), form shadows on the phosphor lines 12b, 12g, and 12r to produce non-light emitting portions 16. The larger the number of the bridges 15, the larger the number of the non-light emitting portions 16, and thus the more the luminance across the phosphor screen decreases. The luminance can be improved simply by setting a pitch Pv in the vertical direction of the apertures 11 to be large so that the bridges 15 are reduced in number. However, this causes the shadows of the bridges projected on the phosphor screen to be perceived by the human eye, and thus the non-light emitting portions 16 are likely to be perceived visually as black stripes, i.e. picture noise.
That is, in the conventional technique, while the luminance across the phosphor screen is low due to the shadows of the bridges, there is a limit to improvements in luminance from the standpoint of picture quality, which has been disadvantageous.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a color picture tube that can achieve excellent picture quality and high luminance.
In order to solve the aforementioned problem, a color picture tube of the present invention includes an envelope composed of a face panel having an inner face on which a phosphor screen is formed and a funnel bonded to the rear part of the face panel, the phosphor screen being formed of a plurality of phosphor lines in the form of stripes, in which a color selecting electrode opposed to the phosphor screen is provided. The color selecting electrode has a plurality of apertures and bridges that separate the adjacent apertures from each other in a direction along the phosphor lines. Electron beams emitted from an electron gun in the funnel hit the color selecting electrode and pass through the apertures to land at the phosphor screen. In the color picture tube described above, in the vicinities of shadows of the bridges formed as a result of projection by the electron beams, each of light emitting regions in which the phosphor lines emit light by irradiation with the electron beams has a part in which a wide portion of a greater width than a basic width of the light emitting region is provided.
In the present invention, xe2x80x9cthe basic width of the light emitting regionxe2x80x9d is defined as a width of the light emitting region in a portion other than both end portions in a longitudinal direction. When the portion of the light emitting region other than both the end portions can be deemed to be substantially even in width, xe2x80x9cthe basic width of the light emitting regionxe2x80x9d refers to the width of the light emitting region in the portion other than both the end portions. When the portion of the light emitting region other than both the end portions is uneven in width (without consideration of an unintended fault caused in the manufacturing process), xe2x80x9cthe basic width of the light emitting regionxe2x80x9d refers to a width of the light emitting region in a portion having the smallest width or a width of the light emitting region in the midsection in the longitudinal direction.
According to this configuration, when the color picture tube is in operation, darkening of the phosphor screen can be compensated, which is caused by the shadows of the bridges shading the phosphor lines. Thus, a color picture tube can be provided that can prevent a decrease in the luminance of a phosphor screen and picture noise that are caused by shadows of bridges, and can achieve excellent picture quality and high luminance.
In the color picture tube of the present invention, preferably, in the vicinities of the shadows, each of the phosphor lines has parts in which a wide portion of a greater width than a basic width of the phosphor lines is provided.
According to this configuration, the light emitting regions, each having the part in which the wide portion is provided, can be obtained easily.
Furthermore, in the color picture tube of the present invention, preferably, an area S1 of an auxiliary light emitting region, which is obtained by subtracting an area of a basic width light emitting region having a width corresponding to the basic width from an area of the wide portion of the light emitting region, and an area S2, which is a basic width non-light emitting region having a width corresponding to the basic width as a part of a non-light emitting portion shaded with the shadow of the bridge, satisfy the relationship: 0.9xe2x89xa6S1/S2xe2x89xa61.1. The area S1 of the auxiliary light emitting region is defined, for example, when with respect to each shadow of the bridges, the wide portion is formed on both sides in a vertical direction, as a total area of the auxiliary light emitting regions in both of the wide portions.
Moreover, in the color picture tube of the present invention, preferably, a length Lw of the wide portion in the vertical direction and a pitch Pv of the apertures in the vertical direction satisfy the relationship: 0 less than Lw/Pvxe2x89xa60.1. The length Lw of the wide portion in the vertical direction is defined, for example when with respect to each shadow of the bridges, the wide portion is formed on both sides in the vertical direction, as a distance between an upper end of the wide portion on the upper side and a lower end of the wide portion on the lower side.
According to this configuration, a difference in luminance can be suppressed, which is likely to be caused considerably in the vicinities of the shadows of the bridges.
Furthermore, in the color picture tube of the present invention, preferably, each of the apertures of the color selecting electrode has a protrusion protruding in a horizontal direction at least at one end portion in the vertical direction.
According to this configuration, the phosphor lines, each having the parts in which the wide portion is provided, can be formed easily. Alternatively, the light emitting regions each having the wide portion in the vicinities of the shadows of the bridges can be formed easily.
Moreover, in the color picture tube of the present invention, preferably, a maximum width W1 of the apertures in the horizontal direction in the protrusion and a width W2 of the apertures in the horizontal direction in the midsection satisfy the relationship: 1.0 less than W1/W2xe2x89xa61.5.
According to this configuration, a color shift caused when the color picture tube is in operation can be suppressed.